Extraction and dewaxing of lubricating oils



Patented Jan. 30, 1934 UNITED STATES EXTRACTION AND DEWAXING OFLUBRICATING OILS Francis X. Govers, Vincennes, Ind., assignor to IndianRefining Company, Lawrenceville, 111., a corporation of'Mainc NoDrawing. Application April 20, 1931 Serial No. 531,597

'4 Claims.

This invention relates to a process for the manufacture of lubricatingoils, and more particularly to a process for the treatment ofwax-bearing hydrocarbon oils to effect removal of their waxconstituents, whereby lubricating oils substantially free from wax areobtained. In a prior application, Serial No. 313,346, filed October 18,1928, now Patent 1,802,942 and entitled, Process for recovery andpurification of lubricating oils from mineral oils, I have described amethod for the manufacture of low cold test oil by the removal of'solidhydrocarbons from wax distillate. The present invention, which is a'continuation in part thereof, relates to the treatment of wax-bearinglubricating oil fractions wherein the removal of the solid hydrocarbonsor wax constituents is carried out in two or more steps.

The invention broadly contemplates the preparation of low cold testlubricating oil fractions from wax-bearing hydrocarbon oils, such as waxdistillate or the like, by a process wherein the oil, which may havebeen subjected to any desired preliminary refining treatment, isdissolved in a solvent possessing the properties of dissolving allhydrocarbons contained therein at elevated temperatures and having aselective solvent action between the liquid hydrocarbons and solidhydrocarbons at relatively low temperatures. The resulting solution isthen chilled to effect precipitation of the solid hydrocarbons, and

the mother liquor of solvent and dissolved liquid hydrocarbons isremoved from the precipitated material by filtration, following whichthe mass of separated solid hydrocarbons and liquid associated therewithis commingled with fresh solvent oil and while maintained in a cooledcondition again subjected to filtration to remove the solvent anddissolved oil from the remaining solid hydrocarbons.

In the prior application, Serial No. 313,346, above referred to, I havedescribed subjecting the wax-bearing lubricating oil to a singledewaxing step wherein the wax-bearing oil is disand of such a naturethat upon cooling a solution of such mineral oil wax distillate in thesolvent liquid to 0 F. and removing the solid hydrocarbons soprecipitated and the solvent liquid the resulting oil has a cold test ofsubstantially 0 F. The resulting solution is then chilled to atemperature at which substantially all of the solid hydrocarbonsseparate, whereupon the chilled mixture is subjected to filtration toremove the solvent and dissolved liquid hydrocarbons, depositing thesolid hydrocarbons in the form of a filter cake of slack wax.

The resulting cake of slack wax' comprises a substantial portion ofsolvent and liquid hydrocarbons retained within the crystalline mass ofwax and which retained oil is not only valuable as a lubricant, but alsoits presence in the wax cake renders the latter unsatisfactory forsweating. I have discovered that this retained 011 adhering in the slackwax is particularly valuable as a lubricating oil for.internalcombustion engines and the'like. It is of a more distinctive paraflinicnature and tends to possess a very flat temperature viscosityrelationship combined with low specific gravity. An importantcharacteristic of this oil is its relatively narrow increase inviscosity between F. and 210 F. as well as between intermediate pointsof temperature as compared with lubricating oils of the prior art andalso as compared with the liquid fractions removed in the initialfiltration and which characteristic is essential in the preparation of asuperior type of lubricant adapted for the lubrication of internalcombustion engines.

It is an object of my invention, therefore, to carry out the dewaxingprocess in successive stages wherein, during the first stage, all of thesolid hydrocarbons may be removed as a wax concentrate or slack wax, andduring a succeeding stage the resulting wax concentrate is mixed withadditional solvent and subjected to refiltration while in a cooledcondition to effect more complete separation between oil and waxconstituents. During the first stage the wax-bearing oil is dissolved ina solvent possessing the property of dissolving all the hydrocarbons atan elevated temperature of say 90 F. and above, and having a selectiveaction between the liquid hydrocarbons and solid hydrocarbons at lowertemperatures. The solution is then cooled toa relatively lowtemperature, as for example, 0 F. or below to effect separation of thesolid hydrocarbons, whereupon the cooled mixture is introduced tofiltering means to remove the solvent liquid and dissolved liquidhydrocarbons and form a filter cake of slack wax composed of solid andsemi-solid hydrocarbons together with adhering solvent and dissolvedliquid hydrocarbons.

During the next stage, the above filter cake is removed andadvantageously commingled with fresh cooled solvent. While substantiallythe same or even lower temperature conditions may be maintained duringthis second step, it may be of advantage, however, to employ slightlyhigher temperatures so as not only to effect complete solution of theadhering liquid but also to dissolve those particularly desirable oilconstituents which, as already mentioned, may exist in close associationwith the solid hydrocarbons separated during the initial dewaxing stepand are removed as a component part of the slack wax. By properlyselecting the temperature conditions under which to carry out each ofthe filtration steps, I am able to obtain lubricating oils possessingdifferent characteristics of gravity, viscosity and pour test as may bedesired. The commingled mixture, which may undergo further chilling ifdesired, is then subjected to further filtration to remove the solventand dissolved oil and form a filter cake of solid hydrocarbons. Theresulting reformed filter cake may be freed of its associated oradhering liquid by washing, in situ, with fresh solvent to therebyproduce a wax cake which, after removal by evaporation of the remainingsolvent retained therein, is in a suitable condition for sweating or fordisposition, as may otherwise be desired.

Furthermore, I have found that by regulating the temperature during thewashing of the reformed slack wax cake,.that is, by washing, for

example, in one or more steps while maintaining suitably differenttemperature conditions in each step, I may effect a selective washing ofthe slack wax whereby the oil originally'retained therein or associatedtherewith is removed in selective fractions, having gravity viscosityrelationships of the particular degree desired.

As an example in the practice of my invention, I dissolve 1,000 gallonsof wax distillate having a viscosity of 450 Saybolt universal seconds at100 F. in 3,500 gallons of a mixture of solvent, consisting ofapproximately 37% acetone and 63% benzol, and cool the solution to 10 F.to effect precipitation of the solid hydrocarbons. The cooled mixture ofdissolved oil and solid matter suspended therein is introduced to afilter press, advantageously of the rotating leaf type, wherein thesolvent and dissolved liquid hydrocarbons are removed and a filter cakeof slack wax of desired thickness is formed on the filter leaves, afterwhich filtration is stopped and the liquid content blown back ordisplaced with gas which latter also serves to displace liquid from thefilter cake and so dry it. The resulting filter cake comprisingapproximately 740 gallons of slack wax, of which approximately 280gallons represents solid andretained liquid hydrocarbons, is removedfrom the press and transferred to a tank or other suitable container,provided with stirring apparatus, wherein the slack wax is thoroughlycommingled with 1,110 gallons of solvent similar to that used in theinitial filtering operation, the temperature of the mixturebeing'maintained or regulated by passage through suitable cooling coils.

The resulting mixture of oil at a temperature of 0 F. or below is thenpumped into a second filter to separate the solvent and dissolved liquidhydrocarbons from the solid hydrocarbons.

When a cake of desired thickness is obtained, the liquid contents of thestill may be displaced by blowing with gas, as explained above, and vthe reformed cake 'of solid hydrocarbons is then washed by passingapproximately 2,400 gallons of cold solvent liquid through the cake, inorder to remove entrained liquid and produce a substantially oil-freesweatable cake.

Depending on the character of the wax-bearing oil undergoing treatment,the initial wax cake may be of such a nature that the adhering orretained liquids contained therein may be separated without the additionthereto of appreciable amounts of additional solvent liquid, and bysubjecting the slack wax which already has substantial amounts ofsolvent associated with it, to a pulping action by stirring or agitationso as to disrupt the structure of its crystal mass whereby theseparation of the occluded liquid is facilitated. The disrupting actionobtained by subjecting the cake to such stirring or agitationfacilitates separation of liquid occluded or retained in the mass ofcrystalline wax, thereby permitting its more ready removal from thesolid hydrocarbons during the subsequent filtering step or effecting itssubsequent removal during Washing of the resulting filter cake with aminimum of solvent wash liquid.

One of the most necessary qualities in a sweatable wax is that ofuniformity; not only must it have the right crystalline structure withnot over a definite percentage of sweatable oil, but in addition itsretained oil must be uniformly distributed throughout rather thansegregated into spots since such segregation of the oil in spots tendsto bring about solution of wax in the oil in such spots rather thanpermitting uniform sweating of the oil from the crystals. Thissegregation is the result of non-uniform size and distribution of thecrystals formed during precipitation of the wax from the solvent used,and these non-uniform crystals tend to distribute themselves unevenly onthe filtering surface and thus, whether pressure is applied in order toget a fairly dry cake, or the cake is washed with solvent in order towash out entrained liquid, this unevenness of size and distribution ofcrystals frequently results in wax cakes that are not sweatable. I havefound that by subjecting the cake to mechanical working the crystalstructure of its mass can be readily changed into a form that is easilyfilter pressable or easily washed in a filter press of the rotating leaftype. This change in structure is readily accomplished byremoving thecake from the original filter means and agitating or stirring it inorder to produce uniformity of crystal size and facilitate evendistribution of its constituent parts on refiltration. This uniformsizing of the crystals is advantageously performed in the presence ofadded chilled solvent liquid.

The filtrate produced in the initial filtration stage will containapproximately 72% of the total available amount of pressed distillate orfiltered oil, and such oil, after removal of the solvent, will have acold test of approximately 5 F. The filtrate produced from thefiltration of the commingled slack wax and solvent liquid, which willcontain a substantial amount of oil of a desired pour point, may be'mixed with the filtrate resulting'from the initial filtration step,although as I have already set forth, this oil may be disposed of tobetter advantage in a different manner and for different purposes, sinceit possesses certain desirable viscosity characteristics.

The washed cake is removed to a still where the solvent is evaporatedoff and recovered and the wax with the solvent removed is run to sweatpans and sweated in the usual manner to the desired melting point. Therecovered solvent, together with all or aportion'of that recovered fromthe washing of the cake while in the filter, may be used in dissolvingfresh charge to the system. The last portions of Wash solvent passingthrough the cake will contain very small amounts of dissolved oil andmay, therefore, be used for dissolving either fresh charge or slack waxwithout first removing its dissolved oil content.

While the example described sets forth one mode of operation, theinvention is not restricted to any particular set of operatingconditions, such as those of temperatures, etc., and I may find it ofadvantage to employ different temperatures, or vary the temperaturesmaintained during'succeeding steps of the operation for the purpose ofobtaining products possessing different characteristics as may bedesired.

Obviously many modifications and variations of the invention, ashereinbefore set forth, may be made without departing from the spiritand scope thereof, and therefore only such limitations should be imposedas are indicated in the appended claims.

I claim:

1. The process of manufacturing low cold test lubricating oil whichcomprises mixing a waxbearing mineral oil with acetone and benzol insuch a ratio to each other and to the said mineral oil that the acetoneand benzol together at temperatures of approximately 100 F. havesubstantially complete solvent action on such wax-bearing mineral oiland at temperatures of -5 F. and below, have substantially completesolvent action on the liquid hydrocarbons therein but substantially nosolvent action on the solid hydrocarbons therein and upon removal ofsolid hydrocarbons and the acetone and benzol such mineral oil has acold test of substantially the same as the temperature of the mixture atthe time of the removal of the solid hydrocarbons, cooling the mixtureto a temperature at which a concentrate comprising wax and hydrocarbonsof relatively flat viscosity-temperature relationship is formed,filtering from the mixture the mother liquor of solvent liquid anddissolved oil, mixing the resulting concentrate with additional coolsolvent, introducing the mixture to filtering means, filtering from themixture the solvent liquid and dissolved oil, and removing adhering andentrained liquid hydrocarbons from the cake by washing the cake, insitu, with solvent liquid.

2. The process of manufacturing low cold test lubricating oils ofdesired viscosity-temperature relationship by dewaxing wax-bearingmineral oil in stages comprising dissolving the wax-bear- .ing oil in aselective solvent comprising acetone and benzol mixed in substantialproportions, cooling the solution to a temperature of 0 F. or below toform a semi-solid concentrate of wax and hydrocarbons of relatively fiatviscosity-temperature relationship, separating the concentrate from thecold mixture, mixing the concentrate with fresh solvent acetone andbenzol liquid mixture to dissolve the oily constituents of desirableviscosity-temperature characteristic, and filtering the cool mixture toseparate the wax therefrom.

3. The process of manufacturing low cold test lubricating oils ofdesired viscosity-temperature relationship by dewaxing wax-bearingmineral oil in stages comprising dissolving the wax-bearing oil in aselective solvent comprising acetone and benzol mixed in substantialproportions, cooling the solution to a temperature of 0 F. or below toform a concentrate composed of solid wax and semi-solid hydrocarbonstogether with adhering solvent and dissolved liquid hydrocarbons,separating the concentrate from the cold mixture, mixing the concentratewith fresh sol-- vent liquid to dissolve the oily constituentscharacterized by a fiat viscosity-temperature relationship, filteringthe mixture at a temperature of around 10 F. or below to remove thesolvent and dissolved oil and form a filter cake of slack wax, andwashing the resulting cake with fresh solvent liquid at a temperatureslightly above the filtering temperature in order to substantiallycompletely remove adhering oil from the wax cake.

4. The process of manufacturing low cold test lubricating oils ofdesired viscosity-temperature relationship comprising dissolving thewax-bearing oil in a selective solvent comprising acetone and benzolmixed in substantial proportions, cooling the solution to a temperatureof 0 F. or below to form a concentrate composed of solidwaxa'nd-semi-solid hydrocarbons, together with adhering solvent anddissolved liquid hydrocarbons, separating the resulting concentrate fromthe cold mixture, and washing the concentrate in stages with freshsolvent acetone and benzol liquid mixture at temperatures successivelyincreasing above that at which the concentrate was separated from theoriginal solution in order to dissolve out fractions of contained oil ofdesired viscosity-temperature relationship.

FRANCIS X. GOVERS.

